Aerated Steam Sanitization of Whole Fresh Cantaloupes Reduces and Controls Rind-Associated Listeria but Enhances Fruit Susceptibility to Secondary Colonization.

Recent bacterial illnesses and outbreaks associated with the consumption of fresh and fresh-cut fruit and vegetables emphasize the need to supply produce that is microbiologically safe while retaining its quality and nutrient value. We assessed the capacity of aerated steam to reduce initial levels and control the posttreatment proliferation of a 4-strain mixture of Listeria innocua, a surrogate for L. monocytogenes, and microflora native to the rind of whole cantaloupes. Studies were conducted at the pilot-scale level by passing deliberately contaminated melons through a prototype stainless-steel, continuous-feed heating device. Exposure for 240 s to aerated steam heated to 85 °C achieved a mean reduction in surface-inoculated L. innocua of 3.9 ± 0.6 log10 CFU/cm2 (n = 3) and decreased background microorganisms (yeast, moulds, and coliforms) to undetectable levels. No significant outgrowth of surviving L. innocua or yeast and moulds was observed on heat-treated melons during their storage at 4, 7, and 10 °C for 14 days. Treated fruit continued to respire. Although rind quality was altered, edible fleshy portions remained largely unaffected. Cantaloupe inoculated with L. innocua subsequent to its exposure to aerated steam provided a suitable environment for surrogate growth (mean 3.3 log10 increase in rind density over 10 days at 7 °C), whereas its proliferation was restricted on nonheated cantaloupe (mean 0.7 log10 increase). Steam sanitization provides an effective means for the control of pathogen and spoilage organisms, but the proliferation of surrogate organisms on heated cantaloupes raises concern regarding the impact of postprocessing contamination on consumer health risk. PRACTICAL APPLICATION: Water vapor (steam) at a high temperature can be used to sanitize the surface of fresh, whole cantaloupe melons in a continuous-feed manner. Both Listeria bacteria and spoilage organisms are markedly reduced from initial levels and survivor outgrowth severely restricted during subsequent refrigerated storage. This approach to microorganism control is likely most applicable in situations where rinds and flesh are to be separated immediately via further processing.

Characterizing spatial structure of sediment E. coli populations to inform sampling design.

Escherichia coli can persist in streambed sediments and influence water quality monitoring programs through their resuspension into overlying waters. This study examined the spatial patterns in E. coli concentration and population structure within streambed morphological features during baseflow and following stormflow to inform sampling strategies for representative characterization of E. coli populations within a stream reach. E. coli concentrations in bed sediments were significantly different (p = 0.002) among monitoring sites during baseflow, and significant interactive effects (p = 0.002) occurred among monitoring sites and morphological features following stormflow. Least absolute shrinkage and selection operator (LASSO) regression revealed that water velocity and effective particle size (D 10) explained E. coli concentration during baseflow, whereas sediment organic carbon, water velocity and median particle diameter (D 50) were important explanatory variables following stormflow. Principle Coordinate Analysis illustrated the site-scale differences in sediment E. coli populations between disconnected stream segments. Also, E. coli populations were similar among depositional features within a reach, but differed in relation to high velocity features (e.g., riffles). Canonical correspondence analysis resolved that E. coli population structure was primarily explained by spatial (26.9­31.7 %) over environmental variables (9.2­13.1 %). Spatial autocorrelation existed among monitoring sites and morphological features for both sampling events, and gradients in mean particle diameter and water velocity influenced E. coli population structure for the baseflow and stormflow sampling events, respectively. Representative characterization of streambed E. coli requires sampling of depositional and high velocity environments to accommodate strain selectivity among these features owing to sediment and water velocity heterogeneity.

Effect of hillslope position and manure application rates on the persistence of fecal source tracking indicators in an agricultural soil.

The influence of liquid dairy manure (LDM) application rates (12.5 and 25 kL ha) and soil type on the decay rates of library-independent fecal source tracking markers (host-associated and mitochondrial DNA) and persistent (>58 d) population structure was examined in a field study. The soils compared were an Aquic Haplorthod and a Typic Haplorthod in Nova Scotia, Canada, that differed according to landscape position and soil moisture regime. Soil type and LDM application rate did not influence decay rates (0.045-0.057 d). population structure, in terms of the occurrence of abundance of strain types, varied according to soil type ( = 0.012) but did not vary by LDM application rate ( = 0.121). Decay of ruminant-specific (BacR), bovine-specific (CowM2), and mitochondrial DNA (AcytB) markers was analyzed for 13 d after LDM application. The decay rates of BacR were greater under high-LDM application rates (0.281-0.358 d) versus low-LDM application rates (0.212-0.236 d) but were unaffected by soil type. No decay rates could be calculated for the CowM2 marker because it was undetectable within 6 d after manure application. Decay rates for AcytB were lower for the Aquic Haplorthod (0.088-0.100 d), with higher moisture status compared with the Typic Haplorthod (0.135 d). Further investigation into the decay of fecal source tracking indicators in agricultural field soils is warranted to assess the influence of soil type and agronomic practice on the differential decay of relevant markers and the likelihood of transport in runoff.